Acetylating cellulose



Patented Oct. 23, I934 UNITED sures PATENT OFICE ACETYLATlNG CELLU'LOSEWilliam Knight, Jr.

No Drawing. Application ct0ber 14, 1933, Serial No. 693,683

6 Claims.

Thisinvention is a continuation-in-part of my Serial Number 499,534,filed December 2, 1930.

This invention relates toa process for the production of acetylizedderivatives of cellulose'usually spoken of as cellulose acetate, andspecifically to the product obtained therefrom, as the result ofdisclosuresco'ntained in my pending application referred'to above, andhas for one of its objects the preparation of such acetylated cellulosederivatives of great technical importance by virtue of the fact thatthey possess high tensile strength both in the dry and wetted condition,are of high elasticity and resiliency and produce films and filaments aswell as plastic masses of great stability and of a ready solubility in alarge number of the relatively inexpensive organic solvents and solventcombinations which are readily obtained in commerce.

My product consists of or comprises acetylated '26 Musafibercellulose,or cellulose acetate obtained by the esterification of purified Musafiber cellulose, or alphacellulose' obtained by the proper purificationof Musa fiber or Musa fiber cellulose.

It has been shown, and it is believed is generally recognized in thecellulose and cellulose ester art, that other factors being equal thetensile strength of an esterified cellulose, especially wherein theesterification is an acetylation, is in direct proportion to the initialstrength of the cellulose used as the basic or starting material forthe-esterification process. This is readily exemplified in the fact thatwood pulp cellulose is less expensive than cotton cellulose whenproperly prepared for esterification purposes, wood cellulose acetatespeaking in generalities, being of less strength in the acetated stateand less desirable in other respects than is cellulose acetate preparedfrom cotton cellulose, other factors being substantially equal;

It has been shown that a highly purified cellulose may be obtained fromMusa fiber, and one that is high in alpha-cellulose and relatively lowin hemi-cellulose and other cellulosic bodies of relatively inferiorstrength, and it has furthermore been shown that such alpha-cellulose oralpha-celluloses, especially in the esterified condition, areextraordinarily strong and readily susceptible to esterification undersuch conditions as to transmitthe strength of the original cellulose oralpha-cellulose to the esterified product obtained therefrom, and it isthis esterified product which forms the subject matter of thisinvention.

One of the objects of this invention, therefore,

is the preparation of Musa cellulose acetate from Musa cellulose andespecially the utilization of the product obtained as the result of suchacetylation. I have found that Musa cellulose acetate, that is,cellulose obtained from purified Musa fiber when in the acetylatedcondition may be' obtained with maximum conversion of the desirablequalities of high tensile strength, elasticity,

when the Musa cellulose is acetylated, of which two illustrativeexamples are appended hereto, it being understood however that they aregiven merely for illustrative purposes, and the method or methods may bedeparted from in many particulars, the product obtained being restrictedto the description in the appended claims.

Example I.'Ihree and one-half parts acetic anhydride of commercialstrengthQequivalent to at least 2.90 parts of absolute acetic anhydride,and of requiredpurity are slowly added, prefer ably by means of a sprayand with continual, agitation to one part of bone dry Musa fibercellulose (alpha-cellulose obtained from the purification of Musa fibercellulose), after which is added 3.9 to 4.3 parts glacial acetic acid,agitation being continued and the temperature kept preferably at 20 C.or lower until the cellulose has substantially passed into solution, orat least gelatinized, after which there is atomized on and into the masswhile'being stirred, from 2% to 10% offinely powdered phosphorouspentoxide (phosphoric anhydride). After maintaining the temperature atnot above about 20 C. fora further period of one-half hour after all thephosphorous pentoxide has been added, the temperature is allowed to riseto its normal maximum, where it is kept until a test portion Withdrawnresponds to the tests for the particular grade or kind ofacetylcellulose desired, depending upon the particular use to which thecompleted product is to be put. 'When the acetylation has reached thestage wherein the solution or mass appears homogeneous to the naked eye,and where upon examination with a lens only a small amount ofundissolved or partially dissolved fibers are apparent, the temperatureis allowed to rise to about 50 C. or maintained at that temperatureuntil the viscosity fluidity and other properties desired have beenattained, when acetylating is stopped by the addition of a small portionof water, or water admixed with a cellulose acetate solvent as aceticacid, sufficient Water being introduced to at least convert theremaining acetic anhydride into acetic acid. It is also usual andpreferable to cool the mixture to 20 to 30 desolubility and otherdesirable physical constants,

pending upon the amount of free acetic anhydride contained therein,before the addition of water, for the normal rise in temperature or" theacetylization mass is dependent upon the amount of free or uncombinedacetic anhydride contained therein, the larger the proportion of aceticanhydride, the more heat liberated in the mass upon the addition of therequisite amount of water.

The partial hydrolysis or hydration induced by the addition of water inexcess of that re quired to transform acetic anhydride into acetic acid,and the temperature of subsequent ripening and theperiod of the ripeningphase, is governed by the physical constants desired in the finishedester, as is well known to those skilled in the art to which thisinvention appertains. When the desired solubility condition has beenattained the mass is precipitated by commingling water therewith, usualwith violent. agitation, and the flocculent,white, amorphous,water-insoluble Musa cellulose acetate obtained, is washed toneutrality, stabilized and the moisture removed therefrom, all by waysnow known.

Instead of proceeding .asabove outlined for the esterification of Muse.cellulose, the phosphorous pentoxide admixed with glacial acetic acidmay be first incorporated with the cellulose and allowed to stand withgoverning of term perature for several hours, little or noacetylationtaking place during this step in the process. Then the aceticanhydride, or a mixture of acetic anhydride and glacial acetic acid maybe added if all theacetic acid required has not previously beenincorporated with the cellulose, and subse quent steps in the processcarried out as above indicated.

The product obtained is a white, amorphous, fluffy, neutral, tastelesspowder or masses, in-

:soluble in water and. substantially unaffected Lilli;

organic solvents used for dissolving acetylated cellulose, andoiabnormally high tensile strength and elasticity. However, due to itsaugmented strength (toughness) in the non-esterified and esterifiedcondition, acetylated Musa cellulose in general dissolves slower thandoes other forms of acetated cellulose, but the solubility factor is notdiminished thereby, only a comparatively longer 4, time is required toplace the ester in solution.

Example II.-A mixture of sulfuryl chloride and phosphorus pentoxide,equal weights of each are made, and this added in 2% to 10% based on theweight of Musa cellulose, admixed with acetic acid glacial of the rangeof proportions previously stated, is added slowly to bone dry Musacellulose of high degree of purity with agitation and under temperaturecontrol as previously indicated. After the mixture of sulfuryl chloride,phosphorus pentoxide and acetic acid has been n contact with thecellulose for a period of 1 to 4 hours, during which time little or nocellulose acetylation is found to have taken place, acetic anhydridecommercial equivalent to 2.8 to 3.1

parts absolute acetic anhydride based on the dry weight of the Musecellulose is added, and term or thereabouts, and the mass allowed toremain at the ripening or partial hydration temperature until a testsample withdrawn, precipitated washed to neutralitv and dried, respondsto the tests of solubility, stability, viscosity, etc. desired,depending upon the purpose intended for the finished product. When thisstage is reached, the material is rapidly precipitated by the additionof excess of water, neutralized and dried in the usual manner.

Other examples might be cited wherein Musa cellulose may be acetylatedto a product superior in tensile strength to the acetated product ofwood cellulose or cotton cellulose, which are the only two sources ofcellulose used commercially for cellulose acetylation purposes insofaras I am aware, and also superior in other respects, except as to speedof solution in volatile solvents. However, as is well known, viscosityand solubility may be markedly modified during a step in the acetylationprocess, and Musa cellulose acetate is susceptible to such changes, sothat it is possible by a diminution in viscosity, to augment the speedof solution within relatively wide limits.

As an indication of the relative superiority of Musa cellulose acetateover acetated wood pulp or cotton pulp in the acetated condition, it maybe said that in experiments wherein the three sources of cellulose wereacetated simultaneously under substantially identical optimumconditions, and the operation carried out in substantially the samemanner as above outlined, the following comparative constants werefound, basing acetylated purified wood cellulose as 100, that is, the

standard;

Acetylated Wood Cotton Muss Tensile strength in film form 100 115 135445Elasticity in film form 100 108 112-122 Speed of solution 100 94 88*80Viscosity 100 92 87-78 As 100 104 92-80 Original alphacellulose percent--- 91 98 96-98 Furthermore, solutions in neutral solvents andsolvent combinations have been kept under normal atmospheric conditions'for many months without detectable change or the development ofnoticeable acidity or diminution in tensile strength and/ or viscosity.

What I claim is:

1. As a new article, white, fluffy, inodorous, tasteless, neutral,water-insoluble acetic acid ester of Musa cellulose having substantiallygreater strength in the deposited condition after having. once beingplaced in solution, than similarly prepared'acetated wood celluloseand/or acetated cotton cellulose deposited from a solvent.

2. As a new article neutral, structureless, waterinsoluble Musacellulose acetate, having substantially greater strength in thedeposited condition after having been dissolved and the solvent removedtherefrom, than similarly prepared acetated wood cellulose or acetatedcotton cellulose.

3. As a new article, homogeneous, solvent deposited acetic acid ester ofMusa cellulose having substantially greater strength and slowersolubility than similarly prepared wood cellulose. acetate or cottoncellulose acetate.

4. As a new article, homogeneous, solvent deposited acetic acid ester ofalphacellulose obtained from Musa cellulose having substantially greater6. As a new article, homogeneous, solvent deposited acetic ester ofpurified Musa fiber cellulose, having an elasticity of about 12% to 22%greater than a similarly acetated cotton cellulose or wood cellulose.

EDWARD CHAUNCEY WORDEN, I.

